Design Patterns Explained

Figure 21-1 The relationships between commonality/variability
analysis, perspectives, and abstract classes.
Field Notes
Chapter 21 • Design Patterns Reviewed 311
As you learn patterns, it is useful to look for the following forces
and concepts:
• What implementations does this pattern hide? Thereby allow
ing me to change them.
• What commonalities are present in this pattern? This helps me
identify them.
• What are the responsibilities of the objects in this pattern? As it
may be easier to do my decomposition by responsibility.
• What are the relationships between these objects? This will give
me information about the forces present with these objects.
• How may the pattern itself be a microcosmic example of design
ing by context? This affords me a better understanding of why
the pattern is good design.
Summary
In this chapter I summarized our new perspective on object-oriented
design. I described how design patterns manifest this. I suggested
that it is useful to look at patterns by seeing
Approaches to take
In this chapter